Holographic imaging by simultaneous source and receiver scanning

ABSTRACT

Both a radiation source and a radiation receiver are scanned relative to an object scene under investigation for obtaining holographic information as to the scene. By relating the relative movement of the source and receiver in a predetermined manner, various characteristics of the holographically reconstructed image of the object scene may be controlled. In one embodiment, the source and receiver are locked together and scanned relative to an object scene during the construction of a hologram capable of reconstructing an image of the object scene with twice the resolution that is obtained by ordinary holographic techniques. Apparatus for carrying out this improved scanning technique is disclosed in the embodiment of ultrasonic holography wherein a hologram is constructed directly on photographic film or displayed on a cathode ray oscilloscope.

5: Hated tates atent [1113,632,183

[72] Inventors Kenneth A.Haines OTHER REFERENCES Hockessin,Del-; Kock,Proc. Of IEEE, Vol. 56, No. 2, pp. 238- 239 Bernard P. Hildebrand,Kennewick, Wash. (2/19 3 [21] AppLNo. 744,732

Primary Examiner-David Schonber F d l 15 1968 g gf is 4 i AssistantExaminer-Robert L. Sherman [73] Assignee Holotron CorporatioAttorney-Woodcock, Washbum, Kurtz & Machiewicz Wilmington, Del.

ABSTRACT: Both a radiation source and a radiation receiver [54]HOLOGRAPHIC IMAGING BY SIMULTANEOUS are scanned relative to an objectscene under investigation for SOURCE AND RECEIVER SCANNING obtainingholographic information as to the scene. Ey relating 25 Claims, 13Drawing Figs the relative movement of the source and receiver m a [52] US Cl 350/3 5 predetermined manner, various characteristics of theholographically reconstructed image of the object Scene may be 178/65controlled. In one embodiment, the source and receiver are [51 Int. ClG02b 27/22 locked together and scanned relative to an object sceneduring [50] Field of Search 350/35 the construction f a hologram Capablef reconstructing an image of the object scene with twice the resolutionthat is ob- [56] References cued tained by ordinary holographictechniques. Apparatus for car- UNYTED STATES PATENTS rying out thisimproved scanning technique is disclosed in the 3,461,420 8/1969Silverman 350/35 X embodiment of ultrasonic holography wherein ahologram is constructed directly on photographic film or displayed on acathode ray oscilloscope.

PATENTED JAN 41972 SHEET 1 BF 4 PR/Ol? ART PRIOR ART PRIOR AR? PATENTE-UJAN 4 I972 401F200 mOFOE mwljasz Md HOLOGRAPHIC IMAGING BY SIMULTANEOUSSOURCE AND RECEIVER SCANNING BACKGROUND OF THE INVENTION Recentimprovements in the techniques of holography are well known. Asdescribed in patent application Ser. No. 361,977, filed Apr. 23, 1964,now U.S. Pat. No. 3,506,327, two coherent radiation beams are broughttogether with a finite angle therebetween at a radiation detector toform an interference pattern thereon. For optical holography, theradiation is within the visible region and the detector is usuallyphotographic film which records the interference pattern between the twolight radiation beams. One light beam is modified by the object scene tobe recorded and the other light beam serves as a reference beam. Afterexposure and development of the photographic film, it is illuminatedwith a light beam similar to the reference beam used in constructing thehologram. The reconstructing light beam is diffracted by the recordedinterference pattern into at least one diffracted beam which carriesinformation of the object scene for viewing. The object scene is soviewed in full three dimensions including parallax effects as if theobject scene itself were being viewed.

A further recent improvement in the art of holography involves the useof compressional wave energy in the ultrasonic range and is described inpatent application Ser. No. 569,914, filed Aug. 3, 1966. Two coherentultrasonic beams are caused to interfere with each other at anultrasonic detector illuminated with light to view in the optical domaina full threedimensional representation of the object scene as viewed byultrasonic energy. One ultrasonic beam is modified by the object sceneand the other serves as a reference beam.

A more recent development in the art of holography involves scanning asubstantially point receiver relative to an object scene over a surfacewhere an interference pattern from two radiation beams exists. Thereceived radiation is typically converted to an electrical signal whichmodulates the intensity of a point light source which is scanned over aphotographic film simultaneously with scanning the receiver over itssurface. Furthermore, the reference radiation beam may be eliminated andsimulated electronically by a predetermined electrical wave form beingmixed with the electrical signal output of the scanning receiver. Afterthe photographic film is fully exposed and developed, images may beholographically reconstructed therefrom in the normal manner. A systemof scanned receiver holography used with ultrasonic radiation isdescribed by Preston and Kreuzer in Applied Physics Letters, Mar. 1,1967, Vol. 10, No. 5, page 150.

It has also been found that instead of scanning a receiver, theobject-scene-illuminating source may itself by scanned relative to anobject scene over an area. A substantially point receiver remains fixedrelative to the object scene. Such a technique is described more fullyin copending patent application Ser. No. 662,736, filed Aug. 23, 1967.It should be noted that both the scanned receiver and the scanned sourcetechniques produce holograms with the same characteristics as thoseproduced by ordinary nonscanned holography.

Therefore, it is an object of this invention to devise a method ofscanning in holography which allows choosing undistorted desiredmagnification and resolution in its image.

It is also an object of this invention to produce a scanning systemwhich will provide improved resolution in holographically reconstructedimages.

It is an additional object of this invention to produce a scannedholography technique which will reduce the area that need be scannedwithout reducing resolution of the reconstructed image from what itwould be in ordinary holography.

SUMMARY OF THE INVENTION These and additional objects of this inventionare accomplished by a system wherein the source and receiver aresimultaneously scanned in a predetermined manner relative to the objectscene being recorded. According to one aspect of the invention, thesource and receiver are locked together and scanned over an area,thereby producing a hologram capable of reconstructing an image withtwice the resolution available from a hologram constructed in anordinary manner with an aperture the same as the area scanned. In thealternative, only one-quarter of this area need be scanned to produce ahologram capable of reconstructing an image with resolution equal tothat produced from a hologram constructed in the ordinary manner with anaperture of full area. According to another aspect of this invention, ithas been discovered that the source and receiver may also have avelocity relative to each other if the components of velocity of eachrelative to that of the object scene are related by proportionalityconstants. A hologram so constructed is capable of reconstructing alaterally undistorted image of the object scene with its resolution andmagnification dependent upon this proportionality constant.

For a more detailed disclosure of the invention and for further objectsand advantages thereof, reference should be had to the followingdescription taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 and 1A illustrate thetechnique of ordinary holography in the optical domain.

FIG. 2 schematically illustrates receiver scanning in holography.

FIG. 3 schematically illustrates source scanning in holography.

FIG. 4 illustrates one embodiment of the present invention wherein thesource and receiver are simultaneously scanned while locked together.

FIGS. 5 and 5A illustrate the present invention in its more general casewherein the source and receiver are simultaneously scanned relative toan object scene and over independent areas.

FIGS. 6 and 6A illustrate a comparison between images reconstructedaccording to ordinary holography and those reconstructed according tocertain techniques of this invention.

FIGS. 7, 7A, and 7B illustrate a few of the possible areas that may besimultaneously scanned by a source and receiver in carrying out thetechniques of this invention.

FIG. 8 shows an apparatus for practicing one embodiment of the presentinvention wherein the source and receiver are locked together whilescanned over an area relative to an object scene.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, a basictechnique of optical holography will be briefly reviewed. An objectscene 11 is illuminated by a coherent light beam 13 which is most easilyobtained from a laser light source 15 with a lens 17 in its narrow lightbeam 19 and a pinhole filter 21 placed at the focal plane of the lens17. A beam splitter 23 reflects part of the light of the beam 19 intoanother beam 25 in which a lens 27 and pinhole filter 29 are placed togive a good spherical wave front reference light beam 31. Lightreflected from the object scene 11 in the form of an object modifiedbeam 33 is captured by a detector such as photographic film 35. Thereference beam 31 also illuminates the film 35 while intersecting withthe object bearing beam 33 at a finite angle therewith and forms aninterference pattern between the two beams which is recorded on thefilm. The object scene 11 is shown here to be of the reflective type butis it to be understood that transmittive objects may also be thesubjects of a hologram.

After development of the film 35, an image 37 (FIG. 1A) may bereconstructed from the hologram 35 upon illumination by a reconstructinglight beam 39 which preferably has the same curvature as the referencebeam 31 and further strikes the hologram 35' at the same angle at whichthe reference beam 31 struck the photographic film 35 duringconstruction. The reconstructing light beam 39 is diffracted into atleast one image-carrying beam. In FIG. llA, an observers eye is shown ina diffracted beam wherein light from an image appears to be coming frombehind the hologram 35'. If the wavelength of the reconstructing lightbeam 39 is the same as was used in constructing the hologram and if thecurvature of the light beam wave front is similar to that of thereference beam 31 and if it strikes the hologram at the same angle asthe reference beam, the image 37 will be the same size and at the sameposition relative to the hologram as was the object scene ll duringconstruction thereof. As the wavelength or radius of curvature of thereconstructing light beam 39 is altered, the image 37 will be magnifiedor demagnified and its position relative to the hologram 35 will bechanged.

A further development in holography is shown in FIG. 2 wherein a pointradiation receiver is scanned over an area. An effective point radiationsource 41 illuminates an object scene 43 with an object beam ofradiation 45, which is reflected and diffracted by the object in theform of an object modified beam 47. A radiation receiver 49, such asphotocell for visible light radiation, is substantially a point andscanned over a plane area 51. An electrical connection 53 carries fromthe receiver an electrical signal proportional to the radiation incidentthereon. This electrical signal is utilized to modulate the intensity ofa light source which is scanned across a photographic film to constructa permanent hologram. Although a reference beam coherent with the objectbeam 45 could be interfered with the object-bearing beam 47 in thescanned receiver process, it is preferable in certain circumstances, asshown in FIG. 2, to electronically simulate this reference beam. Areference signal 55 is mixed with the receiver output signal 53 in somesort of well-known electronic mixing unit 57 to produce holographicinformation at the output terminal 59. This holographic output signalmay then modulate the intensity of a substantially point light sourcewhich is scanned across a photographic film in synchronism with thescanning of the receiver 49 to produce a permanent hologram. Thehologram so constructed is capable of reconstructing an image of theobject 43 as if a holographic detector such as photographic film wereplaced in the scanned area 51 and illuminated with the object bearingbeam 47 and an appropriate reference beam.

In some situations it may be difficult or impractical to scan thereceiver over an area and it has been found that the source 41 may bescanned over an area relative to the object 43 and the receiver 49 heldconstant relative to the object, as illustrated in FIG. 3. The source 41is here scanned in some convenient manner over an area 61, with a lightsource modulated in intensity by the electrical signal and the output 59scanned over a photographic film in synchronism with the scanning of thesource 41. The resulting permanent hologram is capable of reconstructingan image of the object as viewed through the plane area 61 by ordinarytechniques.

It will be understood that the aforementioned known techniques ofholography and those of the present invention whose description is tofollow do not depend on the particular wave radiation utilized. Theinvention is applicable to the entire spectrum of electromagneticradiation, including visible light, microwaves, infrared, ultraviolet,X-rays radio waves, etc., and for all ranges of compressional oracoustic radiation including subsonic, sonic, supersonic, ultrasonic,hypersonic, and even phonons. The fundamental requirement for producingholographic information is that the wave radiation utilized must becoherent so that a specific wavelength can be defined. When suchradiation is utilized, the object modified beam and the reference beamcan be mixed together to produce an interference pattern which containsholographic information capable of reconstructing the original objectmodified beam and therefore images of the original object.

It should be further noted that modulated wave radiation may be used toproduce the object modified beam. Such wave radiation, for example, maybe visible light modulated at microwave frequencies or it may beultrasonic radiation modulated at sonic frequencies.

It should also be pointed out that the particular type of receiver ordetector will depend on the particular type of wave radiation utilized.For example, in the case of visible light radiation the receiver 49would be some photosensitive device, whereas in the case of ultrasonicwave radiation the receiver 49 would most likely be a quartz transducer.In either the receiver or source scanning technique as illustrated inFIGS. 2 and 3, the holographic information recorded is essentially thesame as that recorded in the basic holographic technique as illustratedin the optical domain in FIG. 1. Although there are many advantages inthe known scanning techniques of constructing a hologram, the end resultis substantially the same no matter how fine the scan pattern.

As part of the present invention, it has been discovered that if boththe source and receiver are scanned relative to the object, theresulting permanent hologram is capable of reconstructing an image ofthe object with desirable characteristics not available through ordinaryholography and scanning techniques. Referring to FIG. 4, according toone aspect of the invention, a source 63 and receiver 65 aresubstantially coincident and locked together for scanning over a surface69 relative to an object 7 l, the resulting hologram will reconstruct animage with twice the resolution that is available from theaforementioned techniques. The reconstructed image appears to be theobject viewed through the scanned surface 69 except that it appears onlyone-half the distance therefrom.

Referring to FIGS. 6 and 6A, the imaging properties of a hologram madeby locking the source and receiver during scanning may be illustrated.Assume that a square block 73 is an object of a hologram located adistance r from a scanned plane 75 having an aperture dimension A. Ifthe area 75 is simultaneously scanned by locked source and receiver, acollimated reconstructing radiation beam incident upon a permanenthologram 77 will reconstruct an image 79 of the object 73 as shown inFIG. 6A, if the reference beam or electronic simulation thereof used inconstructing this hologram was a collimated beam and of the samefrequency as the reconstructing beam. The lateral magnifications M and Mwill be equal to unity and the front surface of the block will belocated a distance r from the hologram 77 which is equal to one-half rThe magnification in the radial direction, M is one-half. This distortedimage is often of no concern, but it may be corrected by the use ofstandard optical systems or by appropriately enlarging (or shrinking)the hologram 77, or by a combination of both of these techniques.

For locked source and receiver scanning, it has been found that thesmallest resolvable element 8 of a reconstructed image parallel to thedimension A is given by the following expression:

8E( \,r,,)/(2A) (l) where A, is the constructing radiation wavelength.This expression may be recognized as equal to one-half the resolutionelement size in ordinary holography. This doubling of resolution is amuch desired advantage and it further may be recognized from equation(1) that, in the alternative to be able to have the same resolution asin ordinary holography, the area scanned need be only onequarter asgreat.

Instead of the source and receiver being substantially coincident asillustrated in FIG. 4, they may be separated by some distance and stillafford the resolution improvement advantage of locked source andreceiver scanning. However, the image reconstructed will be rotated anamount dependent upon the distance between the source and receiver andthe distance of the individual object elements from the scanned sourceand receiver. By controlling the distance between the source andreceiver, therefore, the view obtained of the object scene may thus becontrolled.

It will be noted that there is no relative velocity between the sourceand receiver during the scanning process in the embodiment of thisinvention hereinabove described with reference to FIG. 4. It has beenfound, however, that certain useful results in controlling resolutionand magnification may be obtained if the source and receiver have motionrelative to each other. The nature of this relative motion also controlsdistortion and astigmatism of the reconstructed image. Referring to FIG.5, consider a plane 81 scanned by a source 83 and a plane 85 scanned bya receiver 87 to form a hologram of an object 89. As in all embodimentsof the present invention, the object is illuminated with a divergingbeam from the point source so that the point source illuminatessubstantially the same portions of the object from all points on thesource scanned surface. In a particular embodiment, the scanned planesare parallel to each other and the velocities of the source 83 and thereceiver 87 are at all times during the scanning process in the samedirection or in opposite directions. With the directional limitations onthe velocity of the source and receiver, it has been discovered that agood quality image will be obtained whose resolution and magnificationdepend upon the ratio of these velocities, which may be designated asthe constant C. The smallest object element capable of being resolvedmay be expressed by the following:

T? ..a.. ,A, 2l where A, is the constructing radiation wavelength,

A is the aperture of the receiver scanned plane 85 in a directionparallel to the resolution element 8,

r, the distance of the source scanned plane 81 from the object, and

r the distance of the receiver scanned plane 85 from the object 89.

It will be noted that if C=l and r =r,, the case where the velocity ofthe source 83 and receiver 87 are equal, we have resolution capabilityas described with respect to FIG. 4, and equation (2) becomes equation(1). It may also be noted from equation (2) that if either source or thereceiver remains fixed relative to the object, C==0 and equation (2)becomes the resolution expression of ordinary holography.

Therefore, the resolution capability of a hologram constructed bysimultaneous scanning of the source and receiver is dependent upon theirrelative velocities and may be chosen for any desired resolution betweenthat obtained in ordinary holography and that possible by locked sourceand receiver scanning as described with respect to FIG. 4. Furthermore,as this relative velocity constant C is altered, so the magnification ofthe image is altered. The lateral magnification of the image isundistorted, but there will be unequal magnification in the radialdirection according to the equation:

j& 92. a is).

if r,,= where A is the hologram-reconstructing wavelength. Suchdistortion is often of no concern, but it may be corrected by the use ofstandard optical systems or by appropriately enlarging (or shrinking)the hologram, or by a combination of these techniques.

So far, the embodiment of the present invention described with referenceto FIG. 5 wherein the source and receiver are scanned relative to anobject and with a relative velocity between them has been restricted toparallel plane surfaces scanned with a source and receiver alwaystraveling in the same or opposite direction and the ratio of the sourceand receiver velocities at all times is the same constant C. That is,the source and receiver scan their respective surfaces in patterns thatare replicas of each other. This set of conditions results in alaterally distortionless and nonastigmatic image. It may not bepossible, in certain circumstances, to maintain these conditions exactlybecause of mechanical limitations in scanning equipment or for otherreasons. For instance, the ratio of velocities of the source andreceiver may be one conslant in one direction of scanning and anotherconstant in a transverse scanning direction. The lateral magnificationof the resulting image will then be different in each of the twotransverse scanning directions, and an astigmatic image will result inthat the image will not come to focus in both directions at the sameplane. Furthermore, if the ratio of velocity components is not aconstant, but rather some acceleration exists, the distortion may beeven greater. This distortion may be of no concern in certaincircumstances, and in others it may be corrected by optical elements.

The present invention may be described in a more general manner withreference to FIG. 5A. A plane surface 92 is scanned with a source 93 anda plane surface 94 is scanned with a receiver 95 in order to construct ahologram of an object 91. As opposed to the embodiment of the inventiondescribed with reference to FIG. 5, the source and receiver scanningsurfaces are not here parallel planes.

The embodiments of this invention have been described with surfacesscanned being planes surfaces, but it should be noted that the scannedsurfaces may take on some other shape. For instance, if a flat hologramis constructed by scanning the receiver over a spherical surface, therewill be some effect upon the image reconstructed which may be desirableor may be corrected by optical techniques if undesirable.

It should be noted that throughout the discussion pertaining toscanning, the velocities referred to are those of the source andreceiver relative to the object. It is understood that in fact thesource or receiver may be held fixed relative to its surroundings andthe velocities are then equivalent to relative velocities obtained bymoving the object and receiver or source.

Referring to FIGS. 7, 7A and 78, a few of the many possible areas thatmay be scanned by a source and receiver simultaneously are shown in planview. In FIG. 7 a square area 97 enclosed by the solid lines is scannedby, for example, the receiver. An area 99 enclosed by the dotted linesis scanned by a source. A typical scanning situation will be one inwhich the source and receiver move across their respective areas with aconstant velocity and taking the same amount of time to transverse eacharea, thereby having different velocities. That is, the scanningpatterns of the source and the receiver are replicas of each other.Therefore, the ratio of velocities that is important to know indetermining the characteristics of the resulting image is dependent uponthe relative size of the areas scanned by the source and receiver underthese limited circumstances. Square areas are shown in FIG. 7 to besuperimposed upon one another and FIG. 7A shows another arrangementwhere the areas can be rectangular with proportional dimensions and notsuperimposed upon each other. It can be seen that any number ofcombinations exist for simultaneous source and receiver scanning.

A further possibility is to scan a circular area by a rotating sourceand receiver as shown in FIG. 7B. Consider an area 101 to be scanned bya receiver 103 and an area 105 to be scanned by a source 107. If thesource and receiver have equal angular velocities and are synchronizedto be corresponding angular positions at any instant of time, and iffurther the receiver 103 and source 107 have radial velocities which arerelated by a constant, a hologram may be formed capable ofreconstructing an image without distortion. It should be noted that theparticular areas chosen to be scanned will generally depend uponmechanical feasibility or desirability in scanning one type of area oranother.

Referring to FIG. 8, an apparatus for implementing the techniquesaccording to one aspect of the present invention is illustrated in anembodiment of ultrasonic holography. A source transducer 111 andreceiving transducer 113 are scanned across a hologram aperture area 115to construct a hologram of an object 117. A tank 119 contains anultrasonicenergy-transmitting medium 121 which is generally water forconvenience. The bottom 123 of the tank 119 is preferably constructed ofa thick slab of ultrasound-absorbing rubber to substantially preventreflections back to the receiver 113 from anything except the object117. The source and receiving transducers 111 and 113 are placed belowthe surface of the water 121 in order to avoid any reflection lossesfrom that surface.

A mechanical system for scanning the source and receiver over a hologramaperture may be any one of many possible systems. One such system shownin FIG. 8 utilizes a positioning block 1437 to which the source andreceiver transducers are rigidly attached. A guide rod 149 allows thepositioning block 147 to move along its length and also serves toprovide motive power to the block in a direction transverse thereto. Amotive block 151 is attached to one end of this rod for providing suchtransverse motion. The block 151 is threadedly attached to a worm driverod 153 so that it is moved axially along the drive rod upon rotationthereof. Motion of the block 147 along the guide rod 149 is provided bya guide rod 155 which is operably connected to a motive block 157 whichin turn is threadedly attached to a worm drive rod 159. As the drive rod159 is rotated, the motive block 157 moves axially therealong and thepositioning block 147 follows.

Drive rod 159 is joumaled through the container 119 and has a pulley 161attached to the end thereof. A parallel guide rod 163 (partially hiddenfrom view) has a pulley 165 attached thereto. A chain links these twopulleys with a motor source 167 which may be of any convenient type. Theguide rod 153 and a parallel guide rod 169 (partially hidden from view)have pulleys 171 and 173 attached, respectively, and joined to a motorsource 175 by a chain.

This mechanical system as schematically outlined in FIG. 8 has beenfound to allow rapid scanning of a hologram aperture. In order tominimize the inertia of the system, the worm drive rods 153 and 159contain small steel balls in contact between the rods and motive blockswhich recirculate around the motive blocks 151 and 157 as the blocks aremoved along the rod. This reduces friction of the system and providesquick response.

A motor control circuit 177 is chosen to be compatible with the motorsused and is electrically connected thereto. One such control may includelogic circuitry, and pulse generators designed to drive each of themotors 167 and 175 are driven independently by current pulses calculatedto rotate each of the worm drive rods a fixed amount. Therefore,determining the frequency of pulses applied to each motor allowsdetermination of the relative movement in the transverse directions.

The source and receiver transducers 111 and 113 are circular ceramicelements with a diameter of from 4 to 10 wavelengths of the ultrasoundbeing utilized in water. The transducer element itself is preferablyembedded behind a thin epoxy layer in the end of a small diameter tube.The wavelength of ultrasonic energy utilized may be chosen to dependupon the type of objects to be imaged and their reaction to ultrasoundat various wavelengths. For surface characteristic rendition ofreflective objects, for instance, a frequency in the neighborhood of 10MHz. has been found to be satisfactory.

An electronic oscillator 125 generates the desired frequency for drivingthe source transducer 1 11. This oscillator can be any commerciallyavailable type within the frequency range desired and should have arelatively stable output and high degree of temperal coherence. Since anoscillators output is generally not of sufiicient amplitude to drive atransducer directly, a radiofrequency power amplifier 127 is employed toincrease the amplitude of the signal.

It should be noted that an advantage of scanned ultrasonic holography ingeneral over ordinary ultrasonic holography as disclosed in theaforementioned copending patent application Ser. No. 569,914, is thatsubstantially less ultrasonic energy is required to construct ahologram. In ordinary ultrasonic holography, there must be sufficientenergy to produce a standing wave pattern in an area detector whichgenerally requires overcoming surface tension of a liquid.

The ultrasound reflected from the object 117 is then detected by thereceiver 113 and converted into electrical signals which are amplifiedby a radiofrequency amplifier 129. The amplified signal provides anelectric analog, in amplitude and phase, of the ultrasound field atevery point in the scanned plane.

Since a reference ultrasonic beam was not used within the ultrasonictransmitting medium 121, an electrical signal must be mixed with theoutput signal of the amplifier 129 in order to electronically simulatean interference pattern. For this, a balanced mixer 13] combines thesignal from the amplifier 129 with a reference signal from theoscillator A type of phase sensitive detector is preferred for use asthe balanced mixer 131 and a product detector type has been found tohave many advantages. The output of the balanced mixer 131 is anelectrical analogue of a hologram as if a reference beam has beendirected to the surface of the ultrasonic transmitting medium 121transversely thereto from an area 133. Note then, that the object 117must be placed off-axis in order to construct a hologram without visualinterference of unwanted background radiation. If the object 117 isdesired to be placed within the area 133, then the reference beam mustbe made off-axis and this may be done by placing a phase shifter betweenthe oscillator 125 and balance mixer 131 to operate upon the referenceelectrical signal.

In either case, the electrical output of the balanced mixer 131 is asignal that is nearly direct current but varies sinusoidally with therelative phase between the output signal of the amplifier 129 and thereference signal from the oscillator 125. It is this phase amplitudesignal which, when recorded as transmission variations on photographicfilm, forms the desired hologram. However, this signal is preferablysubjected to some alteration before it is used to construct a hologramon photographic film. A signal processor 133 using normal transistoroperational amplifiers, amplifies this phase amplitude signal, clipssome of larger transient peaks, and shifts the average amplitude of thesignal to correspond with the photographic film sensitivity. Theelectrical signal from the signal processor 133 then drives a lightsource 135 which is scanned across an area 137 as a result of itsmechanical connection to the positioning block 147 which scans thesource and receiver transducers. Thus the light source 135 is scanned inthe same pattern as that of the source 11 and receiver 113. The camera139 will likely expose its film to a demagnified replica of the lightpattern scanned across the surface 137. A camera 139 will allow exposureof its film until the full area 137 has been scanned by the light bulb.Upon development of the film, a permanent hologram is obtained capableof reconstructing an image of the object 117 as viewed by ultrasonicenergy.

As a further refinement in the system which may be desired to improvethe quality of the hologram, a feedback loop is provided to compensatefor the nonlinearity of the light source 135. A photodiode 141 convertsthe intensity of the light source 135 into an electrical signal which isthen fed back into the signal processor 133 so that the bulb brightnessis made a linear function of the phase amplitude signal. For manyapplications, however, this nonlinearity correction is not necessary toobtain a hologram capable of reconstructing an image of acceptablequality.

As an alternative to using a light source directly scanning a film, anoscilloscope 143 is employed to display the hologram in a manner capableof being photographed from the oscilloscope screen by a camera 145. Thephase amplitude output signal of the signal processor 133 is connectedto the oscilloscope 143 to modulate the intensity of the electron beamstriking the face of the tube. The electron beam must be scanned acrossthe tube face in synchronism with scanning of the source and receiver111 and 113 (that is, at a speed related at all times to the source andreceiver speed by a proportionality constant) and may receive the x-yscanning signal from a voltage output of the motor control 177.

By either method, after the photographic film is developed, it isilluminated with substantially monochromatic light which is diffractedby the hologram into two first order diffracted beams, each of whichcarries information as to the object 117. One diffracted beam will bringto focus in space an orthoscopic image of the object 117, while theother beam will bring to focus in a different position in space apseudoscopic image of the object 117.

Although the specific system of FIG. 8 is designed for ultrasonicholography, it will be recognized that similar approaches to holographywith electromagnetic radiation of various types may be taken.

Although the invention as been described in general terms with referenceto simplified embodiments, it will be apparent to those skilled in theart that the underlying principle of this invention represents a broadadvance in the general field of holography. Therefore, it is intendedthat the invention should not be limited to the specific embodiment orexamples described but rather should be construed to include all suchembodiments and applications as fall within the spirit and scope of theappended claims.

What is claimed is: 1. In a method of producing holographic informationof an object which includes the steps of,

illuminating the object by a diverging coherent radiation beam from apoint source, thereby to produce object modified radiation,

scanning a point receiver at a finite velocity over a surface areahaving a finite extent in two dimensions relative to said object todetect the object modified radiation, and

mixing a reference signal with the object modified source radiationstriking said receiver, said reference signal being mutually coherentwith the object-illuminating radiation beam, thereby producingholographic information of the object;

the improvement comprising,

simultaneously scanning the source at a finite velocity over a surfacearea having a finite extent in two dimensions relative to said object.

2. A method according to claim 1 wherein the surface areas scanned aresubstantially plane areas. I

3. A method according to claim 2 wherein the plane surface areas scannedare substantially parallel.

4. A method according to claim 2 wherein the plane surface areas scannedare substantially coincident.

5. A method according to claim 1 wherein the surface areas scanned areparallel plane areas and wherein the source and receiver are scannedover the areas with a ratio of their velocities being substantially aconstant throughout the scanning process.

6. A method according to claim 1 wherein velocity components of thescanning source and receiver relative to said object are related byproportionality constants throughout the scanning process.

7. A method according to claim 6 wherein said source and receiver arescanned over substantially plane areas.

8. A method according to claim wherein the constant relating thevelocities of the scanning source and receiver is unity.

9. A method according to claim 1 wherein said source and said receiverare mechanically locked together throughout the simultaneous scanning.

10. A method according to claim 9 wherein the locked source and receiverare substantially coincident with each other.

11. A method according to claim 1 wherein the step of illuminating theobject by a coherent radiation source includes illuminating the objectby a source of electromagnetic energy.

12. A method according to claim 1 wherein the step of illuminating theobject by a coherent radiation source includes illuminating the objectby a source of compressional wave enery- 13. A method according to claim1 wherein the step of illuminating the object by a coherent radiationsource includes the step of illuminating the object by a source ofvisible light.

14. A method according to claim 1 wherein the source scanned andreceiver scanned areas are nonoverlapping.

15. A method of producing and recording holographic information of anobject, comprising the steps of:

illuminating the object by scanning a point coherent radiation source ata finite velocity over a surface area of finite extent in two dimensionsrelative to said object, said point source illuminating substantiallythe same portions of the object from every point on the scanned surfacearea, thereby to produce object modified radiation,

simultaneously scanning a point receiver at a finite velocity over asurface area having a finite extent in two dimensions relative to saidobject to detect the object modified radiation,

mixing a reference signal with the object modified radiation strikingsaid receiver, said reference signal being mutually coherent with theobject illuminating source radiation, thereby producing holographicinformation of the object, and

recording said holographic information on a two-dimensional areadetector in a form so that a three-dimensional optical image of saidobject may be reconstructed therefrom. 16. A method of producingholographic information of an object, comprising the steps of:

illuminating the object by scanning a point coherent radiation source ina given pattern across a first surface area of finite extent in twodimensions relative to said object, said point source illuminatingsubstantially the same portions of the object from every point on thescanned first surface area, thereby to produce object modifiedradiation,

simultaneously scanning a point receiver in a pattern that is asubstantial replica of said given source scanning pattern over a secondsurface area of a finite extent in two dimensions relative to saidobject, thereby detecting the object modified radiation,

mixing a reference signal with the object modified radiation strikingsaid receiver, said reference signal being mutually coherent with theobject illuminating source radiation, thereby producing holographicinformation of the object, and

exposing to said holographic information a photosensitive surface areaof a finite extent in two dimensions point-bypoint thereacross in apattern that is a substantial replica of said given source scanningpattern, whereby the holographic information produced by scanning saidobject is displayed in a form from which a three-dimensional image ofthe object may be reconstructed.

17. The method as defined in claim 16 wherein the simultaneously scannedsource and receiver have velocity components in at least one directionthat are related by a single proportionality constant throughout thescanning of said source and receiver surfaces.

18. The method as defined in claim 17 wherein said first and secondsurfaces are planes which are parallel to each other.

19. A method of producing holographic information of an object,comprising the steps of:

illuminating the object with a diverging beam of coherent radiation froma point source, thereby generating an object modified radiation wavefront,

positioning in the path of the object modified radiation wave front apoint radiation receiver which generates a signal proportional to theradiation intensity incident thereon,

scanning the source and receiver over respective surface areas of finiteextent in two dimensions relative to the object, said source andreceiver at every instant traveling with respect to the object withvelocities in a common direction and with a ratio of their speedsrelative to the object being substantially a constant throughout thescanning of their respective areas,

mixing a reference signal with the object modified radiation strikingsaid receiver, said reference signal being mutually coherent with theobject illuminating source radiation, thereby to produce a holographicinformation signal of the object,

simultaneously exposing a photosensitive surface area of a finite extentin two dimensions to said holographic information signal, said surfacebeing exposed point-by-point thereacross at a velocity related at alltimes by a proportionality constant to the receiver velocity, wherebythe holographic information signal is displayed in a form from which athree-dimensional image of the object may be reconstructed. 26. Themethod as defined in claim 19 wherein said source and receiver scannedsurface areas are planar surfaces oriented substantially parallel toeach other.

21. The method as defined in claim 19 wherein said source and receiverscanned surface areas are nonoverlapping.

22. A method of producing holographic information of an object,comprising the steps of:

illuminating the object with coherent radiation from a point source,thereby to produce object modified radiation,

detecting the object modified radiation with a point receiver," W V or W3,

simultaneously scanning said point source and said point receiver in alocked relationship over surface areas of finite extent in twodimensions relative to said object,

mixing a reference signal with the detected object modified radiationstriking the receiver, said reference signal being mutually coherentwith the object-illuminating source radiation, thereby producingholographic information of the object, and simultaneously exposing tosaid holographic information a photosensitive surface area of finiteextent in two dimensions point-by-point thereacross in a pattern that isthe same as or a substantial replica of the scanning pattern of saidsource and receiver relative to said object, whereby the holographicinformation is displayed in a form from which a three-dimensional imageof the object may be reconstructed. 23. A method of producing aholographic image of an object, comprising the steps of:

illuminating the object by scanning a point coherent radiation source ina given pattern across a first surface area of finite extent in twodimensions relative to said object, said point source illuminatingsubstantially the same portions of the object from every point on thescanned surface area, thereby to produce object modified radiation,

simultaneously scanning a point receiver in a pattern that is asubstantial replica of said given source scanning pattern over a secondsurface area of a finite extent in two dimensions relative to saidobject, thereby detecting the object modified radiation,

mixing a reference signal with the object modified radiation strikingsaid receiver, said reference signal being mutually coherent with theobject-illuminating source radiation, thereby producing holographicinformation of the object, exposing to said holographic information aphotosensitive surface area of finite extent in two dimensionspoint-bypoint thereacross in a pattern that is a substantial replica ofsaid given source scanning pattern, thereby forming a hologram, and

illuminating said hologram with light radiation to reconstruct an imageof said object.

24. The method as defined in claim 23 wherein the simultaneously scannedsource and receiver have velocity components in at least one lateraldirection that are related by a proportionality constant C at anyinstant throughout the scanning of said source and receiver surfaces,wherein the distances to the source and receiver scanning surfaces fromthe object are equal, and wherein magnifications of the object image ina radial direction (M and in said lateral direction (M,) are madesubstantially equal by making M,F=M in the following expression:

where A, is the wavelength of said coherent object-illuminatingradiation and A is the wavelength of said hologram-illuminating lightradiation,

25. A method of producing holographic information with an objectsubmersed in aliquid medium, comprising the ste s of:

illuminating the ob ect by scanning in said liquid me mm a point sourceof compressional wave energy in a given pattern across a first surfacearea of finite extent in two dimensions relative to said object, saidpoint source illuminating substantially the same portions of the objectfrom every point on the scanned first surface area, thereby to produceobject modified radiation,

simultaneously scanning in said liquid a point receiver of compressionalwave energy in a pattern that is a substantial replica of said givensource scanning pattern over a second surface area of a finite extent intwo dimensions relative to said object, thereby detecting the objectmodified radiation,

mixing a reference signal with the object modified radiation strikingsaid receiver, said reference signal being mutually coherent with theobject-illuminating source radiation, thereby producing holographicinformation of the object, and

exposing to said holographic information a photosensitive surface areaof a finite extent in two dimensions point-by point thereacross in apattern that is a substantial replica of said given source scanningpattern, whereby the holographic information produced by scanning saidobject is displayed in a form from which a three-dimensional opticalimage of the object may be reconstructed.

1. In a method of producing holographic information of an object whichincludes the steps of, illuminating the object by a diverging coherentradiation beam from a point source, thereby to produce object modifiedradiation, scanning a point receiver at a finite velocity over a surfacearea having a finite extent in two dimensions relative to said object todetect the object modified radiatiOn, and mixing a reference signal withthe object modified source radiation striking said receiver, saidreference signal being mutually coherent with the object-illuminatingradiation beam, thereby producing holographic information of the object;the improvement comprising, simultaneously scanning the source at afinite velocity over a surface area having a finite extent in twodimensions relative to said object.
 2. A method according to claim 1wherein the surface areas scanned are substantially plane areas.
 3. Amethod according to claim 2 wherein the plane surface areas scanned aresubstantially parallel.
 4. A method according to claim 2 wherein theplane surface areas scanned are substantially coincident.
 5. A methodaccording to claim 1 wherein the surface areas scanned are parallelplane areas and wherein the source and receiver are scanned over theareas with a ratio of their velocities being substantially a constantthroughout the scanning process.
 6. A method according to claim 1wherein velocity components of the scanning source and receiver relativeto said object are related by proportionality constants throughout thescanning process.
 7. A method according to claim 6 wherein said sourceand receiver are scanned over substantially plane areas.
 8. A methodaccording to claim 5 wherein the constant relating the velocities of thescanning source and receiver is unity.
 9. A method according to claim 1wherein said source and said receiver are mechanically locked togetherthroughout the simultaneous scanning.
 10. A method according to claim 9wherein the locked source and receiver are substantially coincident witheach other.
 11. A method according to claim 1 wherein the step ofilluminating the object by a coherent radiation source includesilluminating the object by a source of electromagnetic energy.
 12. Amethod according to claim 1 wherein the step of illuminating the objectby a coherent radiation source includes illuminating the object by asource of compressional wave energy.
 13. A method according to claim 1wherein the step of illuminating the object by a coherent radiationsource includes the step of illuminating the object by a source ofvisible light.
 14. A method according to claim 1 wherein the sourcescanned and receiver scanned areas are nonoverlapping.
 15. A method ofproducing and recording holographic information of an object, comprisingthe steps of: illuminating the object by scanning a point coherentradiation source at a finite velocity over a surface area of finiteextent in two dimensions relative to said object, said point sourceilluminating substantially the same portions of the object from everypoint on the scanned surface area, thereby to produce object modifiedradiation, simultaneously scanning a point receiver at a finite velocityover a surface area having a finite extent in two dimensions relative tosaid object to detect the object modified radiation, mixing a referencesignal with the object modified radiation striking said receiver, saidreference signal being mutually coherent with the object illuminatingsource radiation, thereby producing holographic information of theobject, and recording said holographic information on a two-dimensionalarea detector in a form so that a three-dimensional optical image ofsaid object may be reconstructed therefrom.
 16. A method of producingholographic information of an object, comprising the steps of:illuminating the object by scanning a point coherent radiation source ina given pattern across a first surface area of finite extent in twodimensions relative to said object, said point source illuminatingsubstantially the same portions of the object from every point on thescanned first surface area, thereby to produce object modifiedradiation, simultaneously scanning a point receiver in a pattern that isa substantial replica of said given source scanning pattern over asecond surface area of a finite extent in two dimensions relative tosaid object, thereby detecting the object modified radiation, mixing areference signal with the object modified radiation striking saidreceiver, said reference signal being mutually coherent with the objectilluminating source radiation, thereby producing holographic informationof the object, and exposing to said holographic information aphotosensitive surface area of a finite extent in two dimensionspoint-by-point thereacross in a pattern that is a substantial replica ofsaid given source scanning pattern, whereby the holographic informationproduced by scanning said object is displayed in a form from which athree-dimensional image of the object may be reconstructed.
 17. Themethod as defined in claim 16 wherein the simultaneously scanned sourceand receiver have velocity components in at least one direction that arerelated by a single proportionality constant throughout the scanning ofsaid source and receiver surfaces.
 18. The method as defined in claim 17wherein said first and second surfaces are planes which are parallel toeach other.
 19. A method of producing holographic information of anobject, comprising the steps of: illuminating the object with adiverging beam of coherent radiation from a point source, therebygenerating an object modified radiation wave front, positioning in thepath of the object modified radiation wave front a point radiationreceiver which generates a signal proportional to the radiationintensity incident thereon, scanning the source and receiver overrespective surface areas of finite extent in two dimensions relative tothe object, said source and receiver at every instant traveling withrespect to the object with velocities in a common direction and with aratio of their speeds relative to the object being substantially aconstant throughout the scanning of their respective areas, mixing areference signal with the object modified radiation striking saidreceiver, said reference signal being mutually coherent with the objectilluminating source radiation, thereby to produce a holographicinformation signal of the object, simultaneously exposing aphotosensitive surface area of a finite extent in two dimensions to saidholographic information signal, said surface being exposedpoint-by-point thereacross at a velocity related at all times by aproportionality constant to the receiver velocity, whereby theholographic information signal is displayed in a form from which athree-dimensional image of the object may be reconstructed.
 20. Themethod as defined in claim 19 wherein said source and receiver scannedsurface areas are planar surfaces oriented substantially parallel toeach other.
 21. The method as defined in claim 19 wherein said sourceand receiver scanned surface areas are nonoverlapping.
 22. A method ofproducing holographic information of an object, comprising the steps of:illuminating the object with coherent radiation from a point source,thereby to produce object modified radiation, detecting the objectmodified radiation with a point receiver, simultaneously scanning saidpoint source and said point receiver in a locked relationship oversurface areas of finite extent in two dimensions relative to saidobject, mixing a reference signal with the detected object modifiedradiation striking the receiver, said reference signal being mutuallycoherent with the object-illuminating source radiation, therebyproducing holographic information of the object, and simultaneouslyexposing to said holographic information a photosensitive surface areaof finite extent in two dimensions point-by-point thereacross in apattern that is the same as or a substantial replica of the scanningpattern of said source and receiver relative to said object, whereby theholographic information is displayed in a form from which athree-dimensional image of the object may be reconstructed.
 23. A methodof producing a holographic image of an object, comprising the steps of:illuminating the object by scanning a point coherent radiation source ina given pattern across a first surface area of finite extent in twodimensions relative to said object, said point source illuminatingsubstantially the same portions of the object from every point on thescanned surface area, thereby to produce object modified radiation,simultaneously scanning a point receiver in a pattern that is asubstantial replica of said given source scanning pattern over a secondsurface area of a finite extent in two dimensions relative to saidobject, thereby detecting the object modified radiation, mixing areference signal with the object modified radiation striking saidreceiver, said reference signal being mutually coherent with theobject-illuminating source radiation, thereby producing holographicinformation of the object, exposing to said holographic information aphotosensitive surface area of finite extent in two dimensionspoint-by-point thereacross in a pattern that is a substantial replica ofsaid given source scanning pattern, thereby forming a hologram, andilluminating said hologram with light radiation to reconstruct an imageof said object.
 24. The method as defined in claim 23 wherein thesimultaneously scanned source and receiver have velocity components inat least one lateral direction that are related by a proportionalityconstant C at any instant throughout the scanning of said source andreceiver surfaces, wherein the distances to the source and receiverscanning surfaces from the object are equal, and wherein magnificationsof the object image in a radial direction (Mr) and in said lateraldirection (Mx) are made substantially equal by making Mr Mx in thefollowing expression: where lambda 1 is the wavelength of said coherentobject-illuminating radiation and lambda 2 is the wavelength of saidhologram-illuminating light radiation.
 25. A method of producingholographic information with an object submersed in a liquid medium,comprising the steps of: illuminating the object by scanning in saidliquid medium a point source of compressional wave energy in a givenpattern across a first surface area of finite extent in two dimensionsrelative to said object, said point source illuminating substantiallythe same portions of the object from every point on the scanned firstsurface area, thereby to produce object modified radiation,simultaneously scanning in said liquid a point receiver of compressionalwave energy in a pattern that is a substantial replica of said givensource scanning pattern over a second surface area of a finite extent intwo dimensions relative to said object, thereby detecting the objectmodified radiation, mixing a reference signal with the object modifiedradiation striking said receiver, said reference signal being mutuallycoherent with the object-illuminating source radiation, therebyproducing holographic information of the object, and exposing to saidholographic information a photosensitive surface area of a finite extentin two dimensions point-by-point thereacross in a pattern that is asubstantial replica of said given source scanning pattern, whereby theholographic information produced by scanning said object is displayed ina form from which a three-dimensional optical image of the object may bereconstructed.